The invention relates to a novel surface texturing to enhance trapping of light in a photovoltaic cell, and methods of making such texturing.
Light enters a photovoltaic cell and generates current. If any light passes entirely through the cell and escapes without being absorbed, cell efficiency is reduced. Thus methods are employed to increase travel distance of light within a photovoltaic cell, including reflecting light from the back surface of the cell and bending light at either the front or back surface. One method to bend light as it enters the cell is to texture the incident surface so that light which enters normal to the cell strikes a face on the surface at an angle which is not normal to the face, and is diffracted as it enters the cell.
In conventional monocrystalline silicon photovoltaic cells, it is well-known to texture the surface using a crystallographic etch. One commonly used etch produces relatively steep faces sloped at 54.7 degrees from horizontal, which provides effective surface texturing for a wafer which is, for example, 150 microns thick or more. In a photovoltaic cell comprising a significantly thinner silicon lamina, however, this style of texturing allows reflected light to escape and presents problems with cell fabrication.
There is a need, therefore, for a method of surface texturing appropriate to a photovoltaic cell comprising a thinner semiconductor lamina.